1. Field of Invention
The invention relates to a map display system, a map display apparatus, and a map display method, wherein map data is transmitted from an information center and thereby updated.
2. Description of Related Art
An in-car map display apparatus with conventional navigation functions uses map data stored on a disc and thereby performs navigation functions particularly such as a route search and route guidance. However, there exist some problems in the use of such disc since data stored on the disc soon becomes outdated because of yearly repair or reconstruction of roads. Such outdated disc with no data about a new open road or about an out-of-service road causes some problems: a desirable route is not calculated, necessary route guidance is not provided, and a latest-revised toll for an expressway is not ascertained. To solve such problems, one approach proposes using up-to-date data retrievable from data servers over the Internet. Further, from an economical point of view, another approach (as described in Japanese Patent Laid-open No. 2001-84493) proposes limiting the amount of data to be retrieved so as not to waste data-transmission expenses and data-transmission time.
In order to avoid wasteful expenses and time, a conventional in-car map display apparatus generally limits and reduces the amount of the data to be retrieved over a network. For example, when retrieving the up-to-date data, data stored in the conventional in-car map display apparatus is compared with data stored in a server in order to determine a version of the data. Further, the conventional in-car map display apparatus retrieves only data about a route related to a user-designated destination.